A total of five servers in Panama and the Ukraine were taken down Tuesday, while the plug was pulled on two servers in the Netherlands over the last few days, Atif Mushtaq, a researcher at FireEye's security lab, said.

FireEye, the Russian Computer Security Incident Response Team and the Spamhaus Project have been playing a cat-and-mouse game with the spammers, who have launched new servers when others are taken down.

"It's a dogfight between the research community and the bot herders," Mushtaq said. Bot herders refer to the operators of the network of malware-infected, commandeered computers in the botnet.

Grum is responsible for more than 17 percent of the world's spam, according to Mushtaq. Most of the spam sells fake Rolex watches and Viagra.

As of late Tuesday, the master server and one command-and-control server were operating in Russia, where Mushtaq believes the spammers are headquartered.